In modern business it is considered routine practice during oral presentations for the speaker to control the audience's attention beyond the spoken word by using an overhead projector to display written, graphical, artistic or other visual material. These overhead projectors only require use of transparent sheets with visual material to be projected imprinted on the transparent sheets. The transparent sheets are typically plastic and measure 8.5.times.11 inches. This is the same size as business typing paper. Such transparent sheets can for example be individually stored in clear plastic envelopes with three holes punched in a tab on one side of the envelope so the transparent sheets can be conveniently carried in loose leaf notebooks. To use the transparent sheets with an overhead projector they do not even have to be taken out of the clear plastic envelopes. The speaker can stand beside the overhead projector and individually lay each transparent sheet on the overhead projector as needed during the presentation.
Often, though, transparent sheets are made with more material for showing to the audience than the speaker wants projected when the transparent sheet is first put on the overhead projector. The normal practice in such situations is to have the speaker position an opaque sheet over the transparent sheet and move the opaque sheet to uncover only that portion of the transparent sheet with imprinted material that is to be projected. Then at the appropriate times the speaker, or an assistant, moves the opaque sheet so additional imprinted material can be viewed as required. This repositioning of the opaque sheet requires the speaker, if he is to move the opaque sheet, to at a minimum interrupt normal eye and head movement so the transparent sheet and opaque sheet can be seen and the opaque sheet can be accurately moved with respect to the transparent sheet. If an assistant is available, then the speaker does not have to so interrupt the presentation. But in those situations where an assistant is not available the speaker has no choice other than to interrupt the presentation or to use multiple transparent sheets so no transparent sheet includes more material than is to be presented at one time. This option is inefficient and depending on the structure of the presentation can be ineffective because uncovering visual material can be coupled with, for example, suspense in the spoken material to provide dramatic effect.